1. Field of the Invention
The present invention generally relates to substrate processing chambers. More particularly, the present invention relates to controlling the temperature of a component of a substrate processing chamber.
2. Background of the Related Art
In the fabrication of integrated circuits, vacuum process chambers are generally employed to deposit films on semiconductor substrates. The processes carried out in the vacuum chambers typically provide the deposition or etching of multiple metal, dielectric and semiconductor film layers on the surface of a substrate. Examples of such processes include chemical vapor deposition (CVD), physical vapor deposition (PVD), and etching processes. For CVD, a variety of gases are introduced into the process chamber and act as reactants which deposit material on the substrate surface. A uniform distribution of gas concentration within the processing chamber is highly desirable to ensure a uniform progression of the process because variations in the gas concentration within the process chamber produce non-uniform deposition across the substrate surface resulting in a non-planar topography which can lead to reduced yield and device failure.
Gas distribution plates are commonly utilized in CVD chambers to uniformly introduce processing gas into the processing chamber. A typical gas distribution plate comprises a showerhead disposed at the top portion of the chamber or as part of the chamber lid. Generally, a process gas inlet is connected to the gas distribution plate to supply the processing gas thereto. The processing gas passes through the gas distribution plate into the processing chamber. The deposition reaction of the processing gas is typically temperature dependent. Thus, the temperature of the gas distribution plate must be maintained at a temperature at which reaction will not take place therewith.
If deposition occurs on the showerhead, it may clog the showerhead holes and disturb the process gas distribution into the chamber, causing uneven processing on the substrate surface, or particulates of the deposition material can flake off from the showerhead and drop onto the substrate surface, rendering the substrate useless. Furthermore, improper temperature of the gas delivery system may cause condensation of the process gas within the gas delivery system, and reduce the amount of process gas reaching the process chamber and resulting in inadequate deposition.
In addition to affecting the delivery of process gas to the chamber, the gas distribution plate temperature also affects the substrate temperature, and thus, the deposited film properties, because of the close spacing between the substrate and the chamber lid/gas distribution plate. Typically, because of the low pressures present in CVD processing, the emmisivity of the gas distribution plate is the primary contributor affecting the substrate temperature. Although the substrate temperature is "controlled" by controlling the temperature of the substrate support, film properties such as resistance (R.sub.s) uniformity and deposition thickness uniformity can be influenced by variations in the substrate temperature caused by showerhead temperature variations.
Currently, "BCS" or Burn-in/Conditioning/Seasoning is the process employed to control the lid/showerhead temperature. Generally, BCS comprises running the plasma process on one or more wafers until the lid and the gas distribution plate reach a steady state processing temperature (when the chamber is burned-in/conditioned/seasoned) while depositing the material throughout the chamber. Typically, the lid and the gas distribution plate are heated gradually by the plasma generated within the chamber during processing until a desired processing temperature is reached and maintained by a balance of heat provided by the plasma less the heat transferred from these components. Alternatively, an active heating element, such as a resistive heater, can be attached to the lid to speed up the heating process to steady state temperatures. Processing at a steady state temperature is desirable because predictable reactions and deposition occur during steady state conditions.
One particular drawback of the BCS method is the "first wafer effect" in which the first few wafers are rendered useless because of temperature inconsistencies which lead to non-uniform processing results between wafers. During the BCS process, the lid and gas distribution plate temperatures are ramped up to the steady state temperature from a cold start or room temperature by the plasma generated in the chamber. Because substrate processing is generally temperature dependent, the temperature variations during the BCS process cause variations in the deposition rate and other reactions on the first few wafers. The inconsistent properties of the film deposited on the first few wafers, as compared to those processed during steady state conditions, renders the first few wafers useless. Temperature variations during processing of different wafers may also cause inconsistent deposition or processing between different wafers of a process run, resulting in undesirable, inconsistent film properties. Also, the BCS process typically is very time consuming and reduces the output because of the preliminary wafers sacrificed in the BCS process.
Undesirable process gas reactions may also occur at the gas distribution plate when the gas distribution plate is heated to too high a temperature by the plasma generated in the chamber. Typically, CVD process gases breakdown at high temperatures, resulting in reduced deposition rate. One attempt to prevent unwanted reaction due to high temperature at the gas distribution plate provides a liquid coolant passage surrounding the showerhead to cool the showerhead by thermal conduction/convection. FIG. 1 is an exploded perspective view of a gas distribution plate having a liquid coolant passage. The gas distribution plate 120 comprises a base 180 and a liquid passage cover 182. The gas distribution plate 120 is a dish-shaped device made of thermal conductive material having a circular, centrally disposed cavity 150 defined by the side wall 152 and a bottom plate 154. A plurality of gas distribution holes 156 disposed on the bottom plate 154 provide the process gas passage into the processing chamber. A beveled lower wall portion 158 joins the side wall 152 with the bottom plate 154. A flange portion 160 projects outwardly in a horizontal plane to form the upper portion of the gas distribution plate 120 and serves to provide engagement of the gas distribution plate 120 with the base plate of the chamber lid. Fasteners such as bolts or screws secure the plate 120 with the base plate of the chamber lid through a plurality of engagement holes 162. A gas injection plate depression 130 is formed in the upper surface of the flange portion 160 to facilitate the mounting of a gas injection cover plate onto the gas distribution plate 120.
The base 180 includes a liquid coolant passage 173 machined or cut out of the base 180 and surrounds the side wall 152. The liquid passage cover 182 is secured and sealed to the base 180 by fasteners or by welding to form the upper wall of the liquid coolant passage 173. The liquid passage cover 182 includes an inlet 170 and an outlet 174, projecting upwardly from the liquid passage cover 182 and having bores 172 and 176 formed therethrough. The liquid coolant passage 173 is not formed as a complete annular passage. A blockage portion 204 is positioned between the inlet portion 206 and the outlet portion 208 of the liquid coolant passage 173 to prevent the liquid coolant from travelling the short arc distance between the inlet portion 206 and the outlet portion 208. Instead, the liquid coolant enters the liquid coolant passage 173 through the inlet portion 206, travels completely around the side wall 152, and exits the channel 186 through the outlet portion 208.
In operation, the liquid coolant is pumped from a liquid coolant supply (not shown) to the inlet 170 on the gas distribution plate 120. Usually, the liquid coolant supply includes a chiller or refrigeration unit that cools the liquid coolant to a particular temperature. Once the liquid coolant enters the gas distribution plate 120, the liquid coolant circulates through the liquid coolant passage 173 to cool the gas distribution plate 120 and exits the gas distribution plate 120 through the outlet 174. The liquid coolant then returns to the liquid coolant supply and is re-circulated through the system. By providing a liquid coolant at a much lower temperature than the processing gas, the liquid coolant can prevent the lid, and thus, the processing gas flowing therethrough, from heating to an undesired level. However, this apparatus is still susceptible to overheating of the lid and the gas distribution plate as the liquid coolant becomes heated and loses its cooling properties because of re-circulation through the system. Furthermore, this apparatus is limited to cooling the lid temperature below at selected temperature and is not capable of controlling the lid temperature to respond and adjust quickly to temperature fluctuations in the lid and showerhead.
The major drawback of the both the BCS and the coolant techniques is the lack of active regulation of the temperature of lid and the gas distribution plate. To maintain the steady state processing temperature, the BCS process relies on passive heating by the plasma generated in the chamber while the liquid coolant apparatus relies on cooling of the gas distribution plate by the liquid coolant. For both of these techniques, the lid and the gas distribution plate still may reach undesirable temperatures during processing. Furthermore, both of these techniques are unable to respond to and actively control temperature fluctuations in the lid and the distribution plate.
Therefore, there remains a need for an apparatus and a method of regulating the temperature of the lid to the chamber and the associated processing gas distributor or showerhead to provide consistent wafer processing and eliminate first wafer effects. Particularly, there is a need for an apparatus and a method for controlling substrate resistance uniformity and deposition uniformity. There is also a need for a temperature control system which responds quickly to temperature fluctuations in the lid and showerhead.